Electrosurgical device

ABSTRACT

An electrosurgical device includes a high dielectric material and at least one conductor arranged relative to the high dielectric material such that, in use, the high dielectric material is disposed between the conductor and target tissue. A second conductor is arranged relative to the high dielectric material such that, in use, the high dielectric material is disposed between the second conductor and target tissue. Each conductor includes a plurality of conductive fingers interleaved, e.g. in a comb-like fashion or as concentric circles. A method for performing electrosurgery includes delivering energy to a target tissue through a high dielectric material. The electrosurgery includes, e.g., ablation, coagulation, or the treatment of skin lesions.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No. 10/747,101, filed on Dec. 30, 2003, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This description is related to surgical devices and methods for applying thermal and/or electrical energy to organic material such as biological tissue to modify characteristics of the tissue for therapeutic purposes. More particularly, the description is related to electrosurgical devices using radio frequency (RF) energy to cut, coagulate, ablate, or otherwise treat tissue during a medical procedure.

BACKGROUND

Surgical instruments employing RF energy for treatment are used in a variety of surgical procedures. Such instruments generally include an RF probe that delivers RF energy to the part of the body to be affected by the electrosurgical procedure.

Present RF probes are typically either mono-polar or bi-polar probes. Mono-polar probes have a single RF electrode. The RF energy of the mono-polar probe passes from the RF electrode through the area to be treated and then returns through a return electrode attached to the body, often a foot or more away. Bipolar probes include two terminals, an active electrode and a return electrode, which are both positioned within the patient at the area to be treated.

SUMMARY

In one aspect, an electrosurgical device includes a high dielectric material and at least one conductor arranged relative to the high dielectric material such that, in use, the high dielectric material is disposed between the conductor and target tissue.

Implementations of this aspect may include one or more of the following features. A second conductor is arranged relative to the high dielectric material such that, in use, the high dielectric material is disposed between the second conductor and target tissue. Each conductor includes a plurality of conductive fingers. The first plurality of fingers is interleaved, e.g. in a comb-like fashion, with the second plurality of fingers. The device includes a RF power generator and a network coupling the first and second plurality of fingers to the RF power generator.

In an illustrated embodiment, a switching network coupling the RF generator to the conductive fingers controls the depth of treatment of the tissue. The switching network has a first state in which an RF electrical field extends to a first length from a tissue treatment surface of the high dielectric material and a second state in which the RF electrical field extends to a second length from the tissue treatment surface, which is longer than the first length.

In another embodiment, each of the conductors includes a set of concentric circles, and the concentric circles are interleaved.

The RF power generator connected to the conductor is configured to provide RF power with a voltage and a frequency sufficient to produce a dielectric barrier discharge plasma at the surface of the high dielectric material. The RF generator is configured to provide RF power at a frequency up to about 20 MHz and a voltage up to about 1500 Vrms. The RF generator is configured to provide RF power with a voltage and a frequency sufficient to result in a current density at a surface of the high dielectric material that is greater than about 0.2 amperes per millimeter squared and that can be as high as about 1.0 ampere per millimeter squared.

The high dielectric material includes a ceramic material. The high dielectric material is a material having a dielectric constant greater than approximately 10, e.g., typically between about 100 and 1000.

In another aspect, a method for performing electrosurgery includes delivering energy to a target tissue through a high dielectric material.

Implementations of this aspect may include one or more of the following features.

The electrosurgery includes ablating or coagulating the target tissue or treating lesions. Delivering the energy includes forming a dielectric barrier discharge plasma; high density RF currents (for thermal treatment); or a high strength RF electrical field (for voltage treatment) at the surface of the high dielectric material. Energy is delivered with a frequency up to about 20 MHz and a RF power density up to about 50 W per millimeter squared.

The target tissue is in either a non-conductive or conductive environment. The target tissue can be a variety of biological tissues such as, e.g., cartilage, muscle, fat, or ligament.

In another aspect, an electrosurgical device includes a high dielectric material and at least one conductor arranged relative to the high dielectric material such that, in use, energy is delivered to a target tissue through the high dielectric material.

In another aspect, RF energy is applied to a target tissue with a conductor without galvanic contact between the conductor and the target tissue or between the conductor and a conductive medium surrounding the target tissue.

In another aspect, an electrosurgical device includes means for providing electrical energy and means for distributing the electrical energy so as to obtain a substantially uniform field distribution, wherein, in use, the substantially uniform field distribution is applied to a target tissue.

In another aspect, an electrosurgical device includes means for providing electrical energy and means for applying the electrical energy to a target tissue such that electric current does not flow through tissue immediately adjacent to the target tissue.

Advantages may include one or more of the following. For example, the present device and method eliminates or reduces the RF return current and high electrical field present in the tissue surrounding the targeted tissue, thereby reducing or eliminating collateral damage. The configuration of the device provides for a stable discharge region that can be ignited regardless of the device's proximity to tissue and with properties that are not dependent on the device's proximity to tissue. The RF energy is distributed evenly due to impedance of the ceramic. The RF energy is concentrated in a very thin layer at the surface of the ceramic. There is no return path of RF current in the tissue. The ceramic prevents concentration of the RF energy in a small region of the treated area.

The apparatus and method are applicable in a wide variety of medical procedures on a wide range of different bodily tissues. The apparatus can be used in electrosurgery in a saline environment or in glycine or air and can be used, e.g., to treat chondromalacia and for surgery on anterior cruciate ligaments.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of an electrosurgical device.

FIG. 2A is a perspective view of a distal portion of the electrosurgical device.

FIG. 2B is a cross-sectional view of the distal portion of the device taken along the line 2B-2B′ in FIG. 2A.

FIG. 2C is a plan view of the distal portion of the device.

FIG. 2D is a plan view showing the assembly of a disc included as part of the distal portion of the device.

FIG. 3 is a schematic diagram showing the connection of electrical energy to the electrosurgical device.

FIGS. 4A and 4B are simulations of the electric field and current density, respectively, at a surface of the distal portion of the device.

FIGS. 4C and 4D are simulations showing the electric field for alternate configurations of the distal portion.

FIG. 5 is a side view showing a use of the electrosurgical device.

FIG. 6 is a schematic diagram showing a switching network for use with the electrosurgical device.

FIGS. 7 and 8 are plan views showing alternate configuration for the distal portion.

DETAILED DESCRIPTION

Referring to FIG. 1, an electrosurgical device 100 includes a handle 105 connected to an elongated shaft 110 and a power cable 120. Power cable 120 includes a power connector 125 for connection to a source of electrical energy such as an RF power generator (not shown). Shaft 110 is hollow and formed from, e.g., an insulative plastic such as Teflon, polyethylene, polystyrene, or other thermally molded plastic, or made from a metal tube.

Shaft 110 has a distal portion 115 that includes an insulated region 205 terminating at a disc 210. Disc 210 is, e.g., approximately 5 mm in diameter and has an overall thickness of between 25 and 60 mils. Disc 210 has a tissue treatment surface 225 and is formed of a high dielectric material, that is, a material having a dielectric constant greater than about 10, preferably between 100 and 1000.

Referring to FIGS. 2A-2C, embedded within disc 210 is an RF antenna 200. The RF antenna 200 is constructed from a first plurality of conductive fingers 215 a interleaved in a comb-like fashion with a second plurality of conductive fingers 215 b such that each one of fingers 215 a is adjacent to one of fingers 215 b. Fingers 215 a and 215 b are embedded in disc 210 and are shown in FIG. 2A as dashed lines. However, FIG. 2C illustrates fingers 215 a and 215 b as solid lines for clarity. Adjacent fingers are equally separated by a distance d, as discussed further below.

The material of disc 210 preferably also has high electrical isolation to limit voltage breakdown between adjacent conductors. This material is preferably resistant to high temperature and the aggressive chemical environment of RF plasmas. Ceramic is an example of a material that is a high dielectric and has good electrical isolation. Some examples of ceramics suitable for use are those made by American Technical Ceramics, One Norden Lane, Huntington Station, N.Y. 11746 with the dielectric designations of CC, EA, or GA.

As shown in FIG. 2A, fingers 215 a are connected to a first lead 220 a that connects fingers 215 a to a first terminal of the RF power generator through power cable 120 and connector 125. Similarly, fingers 215 b are connected to a second lead 220 b that connects conductors 215 b to a second terminal of the RF power generator through power cable 120 and connector 125. Accordingly, fingers 215 a receive one polarity of the RF voltage, while fingers 215 b receive the opposite polarity. Leads 220 a and 220 b pass through the hollow portion of shaft 110 to power cable 120.

Referring to FIG. 2D, disc 210 is, e.g., formed from a first section of dielectric material 210 a and a second section of dielectric material 210 b. First section 210 a has a thickness of, e.g., between 5 to 10 mils and second section 210 b has a thickness of, e.g., between 20 to 50 mils. Sections 210 a and 210 b can have the same or different dielectric constants.

First section 210 a has tissue treatment surface 225 and a second surface 235 opposite from tissue treatment surface 225. Disposed on second surface 235 are conductive fingers 215 a and 215 b. Fingers 215 a and 215 b are disposed on surface 235 using, for example, standard metal deposition and etching techniques.

Second section 210 b of dielectric material 210 b has a surface 245 with trenches or voids designed to receive conductive fingers 215 a and 215 b such that fingers 215 a and 215 b are encapsulated. A bonding technique is used to join surfaces 235 and 245 and to join fingers 215 a and 215 b to trenches 240 to form a single disc 210 with fingers 215 a and 215 b embedded therein. Second section 210 b provides mechanical strength to disc 210 and electrical isolation between conductive fingers 215 a and 215 b. Second section 210 b can also act to distribute heat from the surface 225.

Referring to FIG. 3, fingers 215 a are connected to a first terminal 315 of an RF power generator 305 through lead 220 a. Similarly, fingers 215 b are connected to a second terminal 310 of RF power generator 305 through second lead 220 b.

When connected to RF power generator 305, fingers 215 a and 215 b radiate RF energy as shown by dashed lines 320, which represent the equipotential lines of the electric field, and solid lines 325, which represent the RF vectors of the electric field. The capacitive impedance of disc 210 distributes the RF energy essentially evenly over surface 225. This electrical impedance is a major component in the RF electrical circuit formed by RF power generator 305, leads 220 a and 220 b, disc 210 and conductors 215 a and 215 b. Thus, the surface of disc 210 acts as an RF energy distributing component. As a result, the RF energy density is substantially uniformly spread over surface 225 and is not affected to any significant degree by uneven proximity to the surrounding tissue.

The RF energy is primarily confined to the area in front of surface 225. Consequently, when surface 225 is applied to or near the tissue to be treated, the RF energy is applied primarily to the tissue to be treated, which can, e.g., reduce or eliminate collateral damage.

Different delivery rates of RF energy can be used for various treatments. For example, as described further below, a high RF energy density can be used to ignite a plasma discharge for use in ablating or cutting tissue. In a procedure such as coagulation, on the other hand, the RF energy density is kept low enough to prevent the ignition of a plasma discharge. Coagulation is performed using thermal treatment with a RF current density of up to, for example, about 0.8 A/mm squared. Similarly, an electric field with a low power density can be used to kill cells in a treatment area. This is achieved, e.g., by connecting the probe to a low frequency or a pulsing high frequency, voltage source, such as, a high density pulsed electric field, e.g., a pulsing electric field with a duration of about 1 us to 100 us, a repetition rate from about 10 kHz to 1 Hz, and a voltage field of up to about 200 V/mil (which is equal to 7.9 kV/mm).

Referring to FIGS. 4A and 4B, a simulation, using finite element analysis software, was conducted to demonstrate that the electric field is located primarily at the treatment surface of the dielectric material. For the simulation, copper with an electrical conductivity of 5.8e+07 Siemens per meter was used for fingers 415 a and 415 b and ceramic with a dielectric constant of 650 was used for high dielectric material 410. The simulation was a two dimensional simulation, with the height of the ceramic material 210 being 0.065 inches and the width being 0.36 inches. The spacing from surface 425 to conductors 415 a and 415 b was 0.005 inches. The thickness of conductors 415 a and 415 b was 0.005 inches and the width of conductors 415 a and 415 b was 0.0175 inches. The spacing between conductors 415 a and 415 b was 0.015 inches. The simulation was conducted for a saline environment, using salt water with a dielectric constant of 81 and electrical conductivity of 4 Siemens per meter as the surrounding medium. An RF power source with a voltage magnitude of ±150 V and a frequency of 13 MHz was applied to conductors 415 a and 415 b, with conductors 415 a receiving one polarity and conductors 415 b receiving the opposite polarity. As can be seen, electric field 400 and current density 405 radiated outward from surface 425 to a distance of approximately 10 mils and was confined primarily to the area in front of surface 425.

In the simulation, the two end fingers were spaced farther apart from their respective adjacent fingers in an attempt to make the distribution of the electric field and current density more uniform. Because of the boundary conditions at the edges of material 410, for equally spaced fingers 415 a and 415 b, the distribution of the electric field and current density will be different at the edges of the material than in the central portion. By adjusting the spacing between the fingers at each edge, a more uniform distribution of the RF current and electric field across surface 425 can be achieved.

Unequal spacing can also be used between adjacent conductors so that the RF electric field radiates or extends outward to different distances in different areas of surface 425 or, in other words, an RF field is produced that has different penetration depths in different areas of surface 425. As described, when RF power is applied to fingers 415 a and 415 b, a high concentration of the RF electric field is created at surface 425. The thickness of this field is a function of the distance d between adjacent fingers of opposite polarity. The further apart conductors of opposite polarity are, the further the electric field extends from surface 425. Thus, the spacing of the conductors can be optimized for specific applications.

Referring to FIG. 4C, a simulation was conducted to demonstrate that different penetration depths of the electric field can be achieved with different spacings between adjacent fingers. The width and thickness of the conductors was 7.5 mils and 5 mils, respectively. A first set 430 a of fingers 415 a and 415 b are spaced 7.5 mils apart, while a second set 430 b of fingers 415 a and 415 b are spaced 30 mils apart. The other parameters are the same as those for FIGS. 4A and 4B. As can be seen, the electric field 435 has a first area 440 a above the first set 430 a of fingers 415 a and 415 b that extends out from surface 425 a smaller distance than a second area 440 b of the electric field 435 above the second set 430 b of fingers 415 a and 415 b. The first area 440 a extends approximately 10 mils, while the second area 440 b extends approximately 40 mils.

Referring to FIG. 4D, another simulation was performed to demonstrate that the shape of fingers 415 a and 415 b affects the penetration depth in addition to the spacing between fingers 415 a and 415 b. The parameters are the same as those for FIG. 4C, except that the width and thickness of the second set 430 b of fingers 415 a and 415 b are 17.5 mils and 5 mils, respectively. As shown, increasing the width of the second set of fingers 430 b resulted in the second area 440 b of the electric field 435 extending further from surface 425 than first area 440 a.

A dielectric barrier discharge (DBD) plasma can be ignited at surface 225 when RF energy is applied to conductors 215 a and 215 b. This discharge is particularly applicable when the goal is to cut or ablate tissue. The plasma exists primarily in a thin layer over surface 225. As a result, collateral damage due to the plasma is reduced or eliminated.

The current density needed to ignite the discharge plasma is obtained by adjusting the voltage or frequency of the RF power applied for a given thickness and dielectric constant of disc 210. For example, assuming a current density of 0.2 A/mm² is needed to ignite a discharge, then a voltage and frequency of the RF power applied to conductors 215 a and 215 b equal to 570 V and 5 MHz, respectively, can be used for a thickness of disc 210 equal to 0.125 mm and a dielectric constant of disc 210 equal to 200.

To arrive at this, the following relationship is used: ${V_{RF} \approx \frac{I_{RF}}{\omega\quad C_{cer}}} = \frac{J \cdot A}{\omega\quad C_{cer}}$ where V_(RF) is the RF voltage, I_(RF) is the RF current, which is equal to the current density J times the area A of the high dielectric material through which the current passes, ω is the angular frequency of the RF power, and C_(cer) is the capacitance of the high dielectric material.

The capacitance in picofarads is equal to: $C_{cer} = {8.5 \cdot 10^{- 3} \cdot ɛ \cdot \frac{A}{d}}$ where ∈ is the dielectric constant of material 210 and d is the thickness of material 210 in millimeters, and A is surface area of material 210 in millimeters squared. Thus, the RF voltage V_(RF) becomes: $V_{RF} \approx \frac{J \cdot d}{8.5 \cdot 10^{- 3} \cdot \omega \cdot ɛ}$ For a current density of 0.2 A/mm², a dielectric constant of 200, and a thickness of 0.125 mm (which is equivalent to 5 mils): $V_{RF} \approx {\frac{1.47 \cdot 10^{10}}{\omega}.}$ Choosing a frequency f=5 MHz results in a voltage V_(RF)=570V. The frequency or voltage is preferably chosen in view of other parameters such as the dielectric breakdown of disc 210. For example, if disc 210 has a dielectric strength of 150 V/mils, then for a thickness of 5 mils the dielectric material has a breakdown voltage of 750 V. Accordingly, the above parameters could be used without exceeded the breakdown voltage of disc 210.

The particular parameters required to ignite the plasma in a given environment can be determined as a matter of routine experimentation. The frequency of the RF energy can be up to approximately 20 MHz. Theoretically, frequencies higher than 20 MHz can be used, but in practice such high frequencies are difficult to generate and can cause problems such as interference with other electrical devices. Generally, plasma ignition in saline is achieved with approximately a quarter of the RF field strength required for ignition in air.

Referring to FIG. 5, in use to treat body tissue 505, such as, for example, articular cartilage, surface 225 is placed in contact with a tissue treatment site 510 or near enough to the tissue treatment site 510 that the electric field or plasma discharge region affects the treatment site 510. As a surgeon applies energy to fingers 215 a and 215 b, RF energy is radiated outward and distributed along surface 225, in a pattern similar to that shown in FIGS. 4A and 4B. In a treatment including, for example, ablation of tissue at tissue treatment site 510, the RF power applied to conductors 215 a and 215 b is such that a DBD plasma 515 is formed at surface 225. To ablate an area of tissue, distal portion 115 along with plasma 515 is moved along the desired ablation area of tissue.

Other surgical procedures (e.g., coagulation or treatment of skin lesions) is performed without forming a DBD plasma. Rather, the RF electric field distributed across and extending from surface 225, and/or any thermal energy resulting from the electric field, are used to treat the tissue. The heat is dissipated in the treated tissue limiting any collateral damage to the surrounding tissue.

Thus, during use, RF energy is applied to a target tissue with a conductor such that the RF energy is applied without galvanic contact (i.e., without direct electric contact) between the conductor and the target tissue or between the conductor and a conductive medium surrounding the target tissue. In the implementations shown, the RF energy is applied through the dielectric material without the conductors and being in direct electric contact with the tissue and without the conductors being in direct electrical contact with a conductive medium (e.g., saline) surrounding the tissue.

Referring to FIG. 6, for some electrosurgical procedures it is desirable to have the ability to adjust the penetration depth of the RF field. As described above, different spacings between adjacent fingers provide for different penetration depths of the RF field. A switching network 650 is one example of how to adjust the RF electric field's depth of penetration. RF generator 605, disc 610, and fingers 651 a and 615 b are the same as described in FIGS. 1-3 and fingers 615 a and 615 b are spaced from one another by a distance d₁. Fingers 615 a and 615 b are connected to RF generator 605 through switching network 650 and three leads 620 a, 620 b, and 620 c. Switching network 650 has two switches, switch 630 and switch 635. When first and second switches 630 and 635 are in a high state (not shown), all of fingers 615 a are connected to first terminal 640 of RF generator through both leads 620 a and 620 b, while all of fingers 615 b are connected to second terminal 645 through lead 620 c. In this configuration, the distance between adjacent conductors of opposite polarity is d₁ and an electric field extends a first length from surface 625 of high dielectric material 610.

When first and second switches 630 and 635 are in a low state (as shown), every other one of fingers 615 a are connected to second terminal 645 of RF generator 605 through lead 620 b, while the other fingers 615 a are connected to first terminal 640. Conductors 615 b are not connected to either terminal of RF generator 605. In this configuration, the distance between adjacent conductors of opposite polarity is d₂, which is greater than distance d1. As a result, the electric field extends a second length from surface 625, which is farther than the first length.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, other configurations of electrosurgical device 100 have the insulative material of portion 205 covering the side 230 (FIG. 2A) of section 210, while leaving surface 225 exposed. Also, shaft 110 can be made from other materials and with different configurations. For instance, distal portion 115 can have a ninety degree bend such that surface 225 is side-facing. Other bend degrees are also possible such as, for example, sixty degrees, forty-five degrees, or thirty degrees, or the shaft can be flexible with an adjustable angle.

Other dimensions and shapes of disc 210 can be used, depending on the application and the surface area of treatment. Also, while it may be desirable to use a material for disc 210 with high electrical isolation, the material can have some conductivity. For example, a semiconductor material can be used.

Other configurations of disc 210 can also be used. For example, disc 210 has varying dielectric constants along a length and/or diameter. Referring to FIG. 7, for example, conductors 715 a and 715 b are embedded in disc 710. Disc 710 has three distinct sections, 720, 725, and 730. Each section 720, 725, and 730 is made from a material with a different dielectric constant. Rather than discrete sections, other configurations have gradually varying dielectric constants across a length or diameter.

Further, the second section of dielectric material 210 b can be eliminated and other techniques used to insure electrical isolation between conductive fingers 215 a and 215 b. For example, a coating of glass or other insulating material is applied to surface 235 and conductors 215 a and 215 b to provide electrical isolation between conductors 215 a and 215 b. Alternatively, distal portion 115 is configured such that a vacuum exists at the surface 235 of dielectric 210 a to provide electrical isolation between conductors 215 a and 215 b.

Other configurations of the embedded conductors can also be used. Referring to FIG. 8, for example, conductors 715 a and 715 b are interleaved as concentric circles. Fingers 715 a are connected to one terminal of the RF power generator, while fingers 715 b are connected to the other terminal.

Moreover, electrosurgical device 100 can have other configurations. For example, electrosurgical device 100 is provided with an internal RF generator, and power cable 120 and connector 125 connect the internal RF generator to AC or DC power. Alternatively, in addition to an internal RF generator, electrosurgical device includes an internal battery to power the RF generator. In this case, power cable 120 and connector 125 are eliminated.

The electrosurgical device can be implemented as a self-coagulating surgical blade. When implemented in this manner, dielectric material 210 b is deposited at the surface of a surgical blade for instant coagulation of, e.g., small arteries.

While an electrosurgical device has been described as dimensioned for endoscopic or arthroscopic surgeries, other implementations are dimensioned larger or smaller, depending on the particular application intended. In such applications, the thickness and size of the high dielectric material 210 a is adjusted accordingly

Accordingly, other implementations are within the scope of the following claims. 

1. An electrosurgical device comprising: a high dielectric material; means for delivering energy to a target tissue through the high dielectric material; and means for adjusting a penetration depth of the delivered energy.
 2. An electrosurgical device comprising: means for providing electrical energy; means for distributing the electrical energy so as to obtain a substantially uniform field distribution, wherein, in use, the substantially uniform field distribution is applied to a target tissue; and means for adjusting a penetration depth of the electrical energy.
 3. An electrosurgical device comprising: means for providing electrical energy; means for applying the electrical energy to a target tissue such that electric current does not flow through tissue immediately adjacent to the target tissue; and means for adjusting a penetration depth of the applied electrical energy. 